The present invention, in some embodiments thereof, relates to stent assemblies and, more particularly, but not exclusively, to stent jackets designed to substantially reduce platelet aggregation, thus decreasing, even eliminating dependence on a platelet aggregation reducers.
Stents are now implanted in more than 70% of all percutaneous coronary revascularization procedures and routinely used in peripheral stenotic vasculature, for example stenotic carotid vessels and stenotic organ vasculature.
A typical stent is typically formed with large, mesh-like, apertures that damage surrounding stenotic vessel tissue during stent expansion. During the first two days following stent placement a layer of endothelial cells grows over the stent frame and the vessel, including the damaged tissue. The endothelial cells produce nitrites that prevent emboli and associated sequela in all but 0.8% of a stent-recipient population.
While improving local circulation over the short term, stents do not remove the long-term danger of blockage in the very stenotic tissue that the stents treat as the damaged tissue is prone to form new scar tissue that protrude through the stent mesh, leading to vessel blockage, referred to as restenosis.
Tubular jackets comprising a polymer having small apertures are often deployed with a stent to prevent restenosis through the larger stent apertures. While often preventing restenosis, jacketed stents cause a significant increase in other life-threatening hazards. Groups of cells in the endothelial tissue coating polymer stent jackets are often unstable, presenting a lifetime risk of developing clumps comprising multiple endothelial cells that freely float through the circulation.
Platelets are sticky, irregularly shaped, disk-like blood-born bodies that promote blood clotting and readily sense, aggregate around, and stick to, clumps of free-floating endothelial cells. An embolism of aggregated platelets and endothelial cells presents a health threat that can form at any time following jacketed stent implantation; causing an estimated 2% of all jacketed stent recipients to eventually develop necrosis of vital organs and/or die.
Drug eluting jacketed stents, while reducing restenosis more than non-eluting jacketed stents, may pose and even greater threat of embolitic death than non-drug eluting stents.
(“Late Acute Thrombosis After Paclitaxel Eluting Stent Implantation”: F. Liistro; Heart; September 2001; Vol. 86, pages 262-264.
The tremendous and constant threat of emboli from jacketed stents has resulted in lifetime administration of prophylactic active pharmaceutical ingredients (APIs) including Clopidogrel Bisulfate, herein Clopidogrel, a platelet aggregation-reducing API marketed as Plavix® by Sanofi-Aventis and Bristol-Myers Squibb
Clopidogrel administration is not hazard-free. Clopidogrel is associated with many side effects, including ulcers, skin rashes, syncope (temporary loss of consciousness), myelotoxicity (bone marrow damage), and TTP (thrombotic thrombocytopenic purpura), characterized by spontaneous, formation of assemblyic thrombi that form emboli. The death rate from TTP, even with immediate diagnosis and aggressive treatment, is approximately 30%.
(“Clopidogrel-Associated TTP: An Update of Pharmacovigilance Efforts Conducted by Independent Researchers, Pharmaceutical Suppliers, and the Food and Drug Administration”; Zakarija, M D, et al; Stroke, February 2004, pages 533-537.
Moreover, Clopidogrel may not prevent life-threatening emboli as current data shows that up to 30% of Clopidogrel recipients fail to develop sufficiently reduced platelet aggregation.
(“Resistance To Clopidogrel: A Review Of The Evidence”: Nguyen MSc, Pharm, et al; Journal of the American College of Cardiology; 19 Apr. 2005; Vol. 45, Issue 8, pages 1157-1164).
Moreover, conditions such as hereditary antithrombin deficiency (HD), are that not responsive to platelet aggregate prophylactic APIs such as Clopidogrel. HD patients receiving Clopidogrel pose a unique at-risk population as HD is often diagnosed only following a serious embolitic event.
Further, people stricken with Auto Immune Deficiency Syndrome (AIDS) may actually develop hemophilia as a result of Clopidogrel administration. Within the AIDS population, a sub-population particularly at risk for developing hemophilia includes individuals having low CCR5 (CCR5 Delta 32 homozygous genotype), which is resistant to infection with HIV-1.
Additionally those at risk for acquiring hemophilia appear to be in the population group of immune-suppressed individuals, including geriatrics diabetics and those in the early stages of an HIV infection.
(“Acquired Haemophilia May Be Associated With Clopidogrel” Montaser Haj et al; British Medical Journal August 2004; pages 329:323)
In addition to the health hazards affecting the above-noted population groups, there are significant risks to every jacketed stent recipient receiving lifetime Clopidogrel.
To prevent excessive bleeding in conjunction with virtually any surgery, Clopidogrel administration must be ceased for a significant period of time both pre-operatively and post-operatively. As a result, patients and surgeons are presented with a Hobson's choice of ceasing Clopidogrel administration and risking death from emboli or continuing Clopidogrel and risking embolism-free bleeding, hemorrhage and death.
In general, jacketed stents, while aiding in preventing restenosis, are associated with many significant, as yet unsolved, problems that can result in death.
There is thus a widely recognized need for a stent jacket that does not require the administration of a platelet aggregation reducing API and it would be highly advantageous to have, a stent devoid of the above limitations.